1. Field of the Invention
The present invention relates to a fixing device that is mounted on an image forming device such as an electrostatic copying machine, printer, facsimile, or the like, and which melts and fixes unfixed toner to paper.
2. Background Information
A fixing device known in the prior art is configured so that a fixing roller is heated from the exterior thereof rather than the interior thereof. This type of fixing device generally includes a fixing roller, a pressure roller that is in pressure contact with the fixing roller, and a plurality of heat rollers that are in pressure contact with the fixing roller and have heating means installed therein. The fixing roller includes a core bar that is a hollow tube made of iron, and a silicone rubber that covers the periphery of the core bar. Each heat roller includes a hollow tube made of aluminum whose surface is coated with a fluoropolymer.
This fixing device can shorten the time needed to warm up the fixing roller because the surface of the fixing roller is directly heated, and thus the total warm up time of the fixing device can be shortened. However, the supply of heat to the fixing roller by the plurality of heat rollers will be limited by the small nip width between each heat roller and the fixing roller, and thus the amount of heat supplied will be limited. As a result, it will be necessary to widen the nip width in the event that one wants to further shorten the warm up time of the fixing roller. However, when the nip width is widened, the localized load on the fixing roller will increase, and thus it will be necessary to increase the drive torque of the fixing roller and strengthen the drive system. In addition, damage to the silicone rubber of the fixing roller may accelerate, and thus durability may be harmed.
An object of the present invention is to provide a novel fixing device that will not increase the localized burden on the fixing roller, not harm the durability of the fixing roller, and shorten the time needed to warm up the fixing roller and thus shorten the total warm up time of the fixing device.